Semiconductor processing can typically involve multiple steps for modifying a substrate in some manner. In many steps, a wafer may be exposed to an input source that may alter a layer in some sort of manner. As but a few examples, in the case of a deposition step, an input source may provide one or more dissociated molecules. In the case of an ion implantation step, an input source may be an ion beam. In a photolithography process, an input source may be a light source, or the like.
For some steps, wafer orientation with respect to an input source may not be a concern. However, for other process steps it can be beneficial to orient a wafer at a predetermined angle with respect to an input source. For example, the effectiveness of some process steps may be optimized by orienting a substrate to be essentially perpendicular to an input source.
Provided an input source is sufficiently large in size it can be possible to orient a wafer at a predetermined angle with respect to the input source. One such example is shown in FIG. 5. FIG. 5 is a diagram illustrating a chemical vapor deposition (CVD) system 500. A CVD system 500 may include a reaction chamber 502 in which an input source 504 may be situated opposite to a chuck 506. A chuck 506 may hold a wafer 508 that is to be processed. In the example of FIG. 5, an input source 504 may be a “shower head” type faceplate that is specifically designed to be larger than a wafer 508. Consequently, it can be possible to orient a wafer substrate at a predetermined angle (e.g., 90°) with respect to an input source. As another example, in a sputtering process, an input source may be a target that is larger than wafer. In such a case, a wafer substrate may be situated opposite to the target at a predetermined angle. Thus, some process steps, by providing an input source that is greater in size than a wafer, are capable of orienting a wafer substrate at a particular angle to the input source.
However, in some processes an input source remains smaller than a wafer. Still further, as processing technology has continued to advance, wafer size has grown correspondingly. As a result, there are many conventional process steps in which it may not be possible to orient essentially all portions of a substrate at the same angle (e.g., 90°) with respect to an input source. An example of such a process step is shown in FIG. 6. FIG. 6 is a diagram showing an ion implantation step in a manufacturing process. An ion implantation system 600 may include an ion source 602 that can accelerate a beam of ions 604 toward a wafer holding surface 606. A wafer 608 may be situated on a surface 606 by a chuck system, or the like.
In FIG. 6, an ion source 602 can be smaller than a wafer 608. Consequently, in order to impact the edges of a wafer 608, an ion beam may scatter up to an angle shown as α. Thus, ions from beam 604 can have an angle of incidence that ranges from 90° to an angle show as β. Variations in angle of incidence can lead to variations in a resulting dopant profile within a wafer substrate. This may lead to device properties that are undesirably non-uniform.
Various approaches for providing a more uniform process result have included attempting to manipulate the position of a wafer as it is being processed. However, such approaches tend to average a range of incidence angles with respect to an input source, rather than provide essentially the same incidence angle for an entire substrate.
U.S. Pat. No. 5,218,209 issued to Takeyama on Jun. 8, 1993 discloses an ion implanter having a wafer holding disk that includes curved wafer holding surfaces. Wafers are placed on the curved wafer holding surface, and the wafer holding disk may then be rotated. The resulting centrifugal force can push the wafers against the curved surface, thereby curving the wafers. The curve introduced into the wafers can result in an ion beam being always perpendicular to a wafer surface. A drawback to the approach of Takeyama can be the size and mechanical complexity of a machine. Such equipment may require a relatively large wafer holding disk and equipment sufficient for spinning such a wafer holding disk at a high enough speed to cause a desired curvature.
In order for many processing steps to be successful, a machine may include some way of holding a substrate (e.g., a wafer) in place. Takeyama, described above, includes a wafer holding surface that appears to rely on centrifugal force to hold wafers in place. Alternate approaches may utilize some sort of chuck system, as also noted above.
Chuck systems may include mechanical chucks, electrostatic chucks, or some combination thereof. A mechanical chuck can include a mechanical clamping mechanism for holding a wafer in place. In addition, in environments having some sort of pressure, a chuck may hold a wafer in place using a vacuum source. Mechanical chucks can be undesirable as clamping mechanisms may obstruct an input source, or require certain mechanical pieces be included in a processing chambers. Vacuum chucks typically do not provide sufficient suction in low pressure environments.
Electrostatic chucks (ESCs) can rely on potential differences between a wafer and a chuck surface to provide an attractive force between the two. ESCs may include single electrode (monopole) ESCs and split electrode ESCs. In a single electrode ESC, a wafer may be held at one potential while a chuck may be held at another. A drawback to single electrode systems is that electrical contact to a wafer is typically required. This may not be compatible with certain processes and/or a given wafer state (the wafer is covered with an insulator).
In a split electrode ESC, a chuck may include one or more electrodes at different potentials. A wafer can be inherently at a potential different than one or more electrodes, and thus be attracted to such electrodes. A split electrode may make physical contact with a wafer through an insulating material and/or a semiconductive material. Advantageously, in a split ESC arrangement, a particular potential does not to be supplied to the wafer itself.
While various conventional chuck systems may secure a wafer in place, such systems hold a wafer to a flat surface. Consequently, such systems do not seem capable of orienting essentially all of a substrate at a particular angle with respect to a limited size input source, such as that shown in FIG. 6.
In light of the above discussion, it would be desirable to provide some way of orienting a substrate at a particular angle, such as 90°, with respect to a limited size input source.